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Introduction to the Modern Periodic Table of the Elements

Key Concepts

  • The modern Periodic Table is made up of a series of rectangles.
    Each rectangle provides us with four important pieces of imformation about an element:

    atomic number
    symbol
    name
    atomic weight
    (a) The symbol of the element.

    (b) The name of the element1.

    (c) The atomic number of the element.

    (d) The atomic weight of the element2.

  • The elements are placed in the periodic table in order of increasing atomic number.

  • Horizontal rows of elements in the periodic table are known as periods.

  • Vertical columns of elements in the periodic table are known as groups.

Symbols of the Elements

The symbol of an element is made up of one or two letters3.
The first letter of the symbol is always a capital (upper case) letter.
If there is a second letter it is always a lower case letter.

Examples:

1
H
hydrogen
1.008
The symbol for hydrogen is H not h
2
He
helium
4.003
The symbol for helium is He not he and not hE and not HE

Names of the Elements

The name of the element is given under its symbol.

Examples:

1
H
hydrogen
1.008
Under the symbol H is written the name of the element hydrogen.
2
He
helium
4.003
Under the symbol He is written the name of the element helium.

Atomic Number of the Elements

The atomic number of the element is usually found above the symbol of the element in the periodic table.
The atomic number is always a whole number4

Examples:

1
H
hydrogen
1.008
The atomic number of hydrogen is 1
2
He
helium
4.003
The atomic number for helium is 2

The atomic number of an element tells us the number of protons in the nucleus of an atom or ion of the element.
Example: hydrogen has atomic number 1, there is 1 proton in the nucleus of a hydrogen atom or ion
Example: helium has atomic number 2, there are 2 protons in the nucleus of a helium atom

Atomic Weight of the Elements

The atomic weight of the element is usually shown below the symbol of the element.
It is given as a decimal number without units of measurement5

Examples:

1
H
hydrogen
1.008
The atomic weight of hydrogen is 1.008
2
He
helium
4.003
The atomic weight of helium is 4.003

If the atomic weight is in brackets, the element has only very short-lived isotopes and it has not been possible to determine the atomic weight of the element. The number in brackets is the atomic mass for the most common isotope (isotopic mass).

Example

86
Rn
radon
[222.0]
The atomic weight of the most common radioactive isotope of radon is 222.0

Periods of the Periodic Table

In the modern periodic table, the rectangles containing the information about the elements are arranged in order of increasing atomic number as you read from left to right.
3
Li
lthium
6.941
4
Be
beryllium
9.012
5
B
boron
10.81
6
C
caron
12.01
7
N
nitrogen
14.01
8
O
oxygen
16.00
9
F
fluorine
19.00
10
Ne
neon
20.18

These rows of elements in the periodic table are known as Periods.
Each period in the periodic table has been assigned a number.

Period 1
H   He
Period 2
Li Be   B C N O F Ne
Period 3
                 
Period 4
                                   
Period 5
                                   
Period 6
                                   
Period 7
                                   

The elements hydrogen (H) and helium (He) make up the first period in the periodic table, Period 1.
The elements lithium (Li) to neon (Ne) shown above make up the second period of the periodic table, Period 2.

Groups of the Periodic Table

The periods containing the elements are stacked on top of each other to form vertical columns which are known as Groups.

Each group in the periodic table has been assigned a number between 1 and 18.

The groups are numbered sequentially from left (group 1) to right (group 18).

Group 1
Group 2
Group 3
Group 4
Group 5
Group 6
Group 7
Group 8
Group 9
Group 10
Group 11
Group 12
Group 13
Group 14
Group 15
Group 16
Group 17
Group 18
    He
                Ne
                Ar
                                  Kr
                                  Xe
                                  Rn

The elements helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn) make up a group in the periodic table.

Group 18 contains the elements helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe) and radon (Rn).

Some groups have also been given names:

  • Group 1 is also known as the alkali metals

  • Group 2 is also known as the alkaline earth metals (or alkaline-earth metals)

  • Group 16 is also known as the chalcogens

  • Group 17 is also known as the halogens

  • Group 18 is also known as the noble gases (sometimes also referred to as the inert gases)
2
He
helium
4.003
10
Ne
neon
20.18
18
Ar
argon
39.95
36
Kr
krypton
83.80
54
Xe
xenon
131.3
86
Rn
radon
[222.0]

The Modern Periodic Table of the Elements

The colour of the boxes in the periodic table below shows the standard state of the element (25oC and 1 atmosphere pressure)

  • Solid elements are found in green boxes.
    Most of the elements are solids.

  • Liquid elements are found in lemon boxes.
    There are two liquid elements; mercury and bromine

  • Gaseous elements are found in blue boxes.
    There are eleven gaseous elements; hydrogen, helium, nitrogen, oxygen, fluorine, neon, chlorine, argon, krypton, xenon, and radon.

The colour of the text in the boxes of the periodic table below shows the metallic character of the element:

  • Metallic elements are written in black text.
    Most of the elements are metals.

  • Non-metallic elements are written in red text.
    All the non-metallic elements are found on the right hand side of the periodic table (except for hydrogen).

  • Semi-metals or metalloids are written in orange text.
    Semi-metals lie between the metals on the left and the non-metals on the right of the periodic table.
  Group 1 Group 2 Group 3 Group 4 Group 5 Group 6 Group 7 Group 8 Group 9 Group 10 Group 11 Group 12 Group 13 Group 14 Group 15 Group 16 Group 17 Group 18
Period 1 1
H
hydrogen
1.008
2
He
helium
4.003
Period 2 3
Li
lithium
6.941
4
Be
beryllium
9.012
  5
B
boron
10.81
6
C
carbon
12.01
7
N
nitrogen
14.01
8
O
oxygen
16.00
9
F
fluorine
19.00
10
Ne
neon
20.18
Period 3 11
Na
sodium
22.99
12
Mg
magnesium
24.31
  13
Al
aluminium
26.98
14
Si
silicon
28.09
15
P
phosphorus
30.97
16
S
sulfur
32.07
17
Cl
chlorine
35.45
18
Ar
argon
39.95
Period 4 19
K
potassium
39.10
20
Ca
calcium
40.08
21
Sc
scandium
44.96
22
Ti
titanium
47.87
23
V
vanadium
50.94
24
Cr
chromium
52.00
25
Mn
manganese
54.94
26
Fe
iron
55.85
27
Co
cobalt
58.93
28
Ni
nickel
58.69
29
Cu
copper
63.55
30
Zn
zinc
65.41
31
Ga
gallium
69.72
32
Ge
germanium
72.64
33
As
arsenic
74.92
34
Se
selenium
78.96
35
Br
bromine
79.90
36
Kr
krypton
83.80
Period 5 37
Rb
rubidium
85.47
38
Sr
strontium
87.62
39
Y
yttrium
88.91
40
Zr
zirconium
91.22
41
Nb
niobium
92.91
42
Mo
molybdenum
95.94
43
Tc
technetium
[97.91]
44
Ru
ruthenium
101.1
45
Rh
rhodium
102.9
46
Pd
palladium
106.4
47
Ag
silver
107.9
48
Cd
cadmium
112.4
49
In
indium
114.8
50
Sn
tin
118.7
51
Sb
antimony
121.8
52
Te
tellurium
127.6
53
I
iodine
126.9
54
Xe
xenon
131.3
Period 6 55
Cs
caesium
132.9
56
Ba
barium
137.3
57-71
lanthanoids
72
Hf
hafnium
178.5
73
Ta
tantalum
180.9
74
W
tungsten
183.8
75
Re
rhenium
186.2
76
Os
osmium
190.2
77
Ir
iridium
192.2
78
Pt
platinum
195.1
79
Au
gold
197.0
80
Hg
mercury
200.6
81
Tl
thallium
204.4
82
Pb
lead
207.2
83
Bi
bismuth
209.0
84
Po
polonium
[209.0]
85
At
astatine
[210.0]
86
Rn
radon
[222.0]
Period 7 87
Fr
francium
[223.0]
88
Ra
radium
[226.0]
89-103
actinoids
104
Rf
rutherfordium
[261.1]
105
Db
dubnium
[262.1]
106
Sg
seaborgium
[266.1]
107
Bh
bohrium
[264.1]
108
Hs
hassium
[277]
109
Mt
meitnerium
[268]
110
Ds
darmstadtium
[271]
111
Rg
roentgenium
[272]
112
Cn
copernicium
  114
Fl
flerovium
  116
Lv
livermorium
   
 
Lanthanoids 57
La
lanthanum
138.9
58
Ce
cerium
140.1
59
Pr
praseodymium
140.9
60
Nd
neodymium
144.2
61
Pm
promethium
[144.9]
62
Sm
samarium
150.4
63
Eu
europium
152.0
64
Gd
gadolinium
157.3
65
Tb
terbium
158.9
66
Dy
dysprosium
162.5
67
Ho
holmium
164.9
68
Er
erbium
167.3
69
Tm
thulium
168.9
70
Yb
ytterbium
173.0
71
Lu
lutetium
175.0
Actinoids 89
Ac
actinium
[227.0]
90
Th
thorium
232.0
91
Pa
protactinium
231.0
92
U
uranium
238.0
93
Np
neptunium
[237.0]
94
Pu
plutonium
[244.1]
95
Am
americium
[243.1]
96
Cm
curium
[247.1]
97
Bk
berkelium
[247.1]
98
Cf
californium
[251.1]
99
Es
einsteinium
[252.1]
100
Fm
fermium
[257.1]
101
Md
mendelevium
[258.1]
102
No
nobelium
[259.1]
103
Lr
lawrencium
[262.1]


What would you like to do now?

1The IUPAC recognizes the commonly used alternative spellings for two elements:
The element with atomic number 13 and symbol Al may be spelt as aluminium or as aluminum.
The element with atomic number 55 and symbol Cs may be spelt as caesium or as cesium.
BUT it should be noted that these elements are present in the IUPAC periodic table as caesium and aluminium.

2The IUPAC periodic table uses standard atomic weights and provides the lower and upper bounds of the standard atomic weight for some elements. Debate still rages about whether the term atomic mass, atomic weight, relative atomic mass, relative atomic weight, or standard atomic weight should be used. Don't worry about it, at High School you can treat all these terms as meaning the same thing.

3The exception to this is for elements that have not yet been discovered. These elements are assigned a name based on their atomic number which will have three numbers, so the symbol for these elements has three letters. Once the element has been produced, it will be officially named and given an official symbol. If you are interested in this topic, you can found out more in the September 2012 issue of AUS-e-NEWS.

4A whole number is a counting or natural number, it does not include negative numbers, nor numbers which are fractions or decimals etc.

5Prior to 1961 the unit amu (atomic mass unit) was used. Since then the unit u (unified atomic mass unit) or Da (dalton) have been widely used but neither of these is an SI unit (as defined by the CIPM, International Committee for Weights and Measures). The issue will be further complicated if the dalton is redfined as being 0.001/NA kg since it would no longer be a unit of atomic mass relative to carbon-12. For High School students it is probably best to avoid the problems and use relative atomic mass as a quantity with no units.

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